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Evaluation of the budget for silicic acid in Cascadia Basin deep water

EVALUATION OF THE BUDGET FOR SILICIC ACID IN CASCADIA BASIN DEEP
WATER
by
Tabitha Ann Esther
________________________________________________________________________
A Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(GEOLOGICAL SCIENCES)
August 2008
Copyright 2008 Tabitha Ann Esther

Silicon (Si) is an essential nutrient in the world's oceans, linked to the carbon cycle through uptake by phytoplankton such as diatoms. In seawater, dissolved Si is in the form of silicic acid, Si(OH)4, which can be converted to skeletal material (biogenic Si or bSi) by both autotrophs (diatoms and silicoflagellates) and heterotrophs (radiolarian and sponges). The North Pacific is a region of much interest due to the high silicic acid concentration in deep waters below 2000m (Talley and Joyce, 1992). It has been suggested that Cascadia Basin, an offshore feature located in the Northeast Pacific, may be the source region for the large plume of silicic acid found at depths between 2000m and 3000m in the North Pacific (Talley and Joyce, 1992, Johnson et al., 2006). The enrichment of silicic acid in Cascadia Basin could be caused by (1) high diatom productivity in surface waters that dissolves as it sinks, (2) a high flux of Si from dissolution of biogenic material at the seafloor, (3) slow movement of water exiting the basin which would allow for accumulation of silicic acid in bottom water over time, or (4) high hydrothermal input of silicon from hot vents and cool seeps. This study seeks to identify whether the source of silicic acid enrichment in Cascadia Basin is the dissolution of biogenic sediments or hydrothermal input. Box models using germanium (an analog of silicon) concentrations and heat input will assess the magnitude of possible sources.

EVALUATION OF THE BUDGET FOR SILICIC ACID IN CASCADIA BASIN DEEP
WATER
by
Tabitha Ann Esther
________________________________________________________________________
A Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(GEOLOGICAL SCIENCES)
August 2008
Copyright 2008 Tabitha Ann Esther